This invention relates generally to a cartridge formed by a stack of sealed trays nested within an open carton, the cartridge being usable in conjunction with a hot air oven functioning to quickly reheat pre-cooked meals contained in the trays, and more particularly to a carton whose geometry and whose distribution of wall openings are such as to facilitate the entry of heated air and its circulation throughout the interior of the carton in the spaces between the trays.
A major factor which militates against the success of self-service fast food techniques for pre-cooked meals is that the food to be reheated is necessarily placed in a closed heating chamber which must be opened to obtain access to the product. In a mass-feeding operation in which a large number of heated meals must be stored in readiness for withdrawal by diners, this involves a complicated multi-compartment structure, each with a separate door that must be opened to remove the meal and then closed.
In my above-identified copending application, there is disclosed a fast food service technique and apparatus therefor whereby pre-cooked meals which have been refrigerated may thereafter be reheated and made directly available to customers without degrading the essential texture, flavor or nutritional qualities of the meal. For this purpose, use is made of a hot air oven for heating tray-loaded cartridges, each constituted by a stack of sealed trays containing pre-cooked meals nested within an open carton whose side walls have holes therein to admit heated air. The oven includes a rotating turntable provided with a raised annular shelf for supporting an annular array of cartridges whose carton walls define a hollow center core. A driven propeller is disposed within the core, the space between the shelf and the turntable forming a restricted flow passage whose inlet communicates with the core and whose outlet lies at the periphery of the turntable
In this hot air oven, a heater assembly above the annular cartridge array produces heated air which is blown by the propeller into the hollow core. Because of the flow restriction, there is a pressure build-up within the core and a substantial portion of the heated air is forced through the holes of the cartons to heat the pre-cooked meals in the trays. The remaining portion of the heated air passes through the flow restriction, the air discharged from the outlet thereof being directed upwardly to create an air curtain around the cartridge array, the air then being recirculated. Thus a toroidal flow pattern of heated air fully envelops the heated trays and serves to isolate the trays from the relatively cool ambient air without, however, interfering with direct access to the trays which may be withdrawn from the cartons when the food is at the desired temperature level for service to diners.
In the fast food technique disclosed in my copending application, the trays, when not in the oven, are kept under refrigeration at a temperature just above the freezing point of the pre-cooked food which, in practice, may be in a range of about 20.degree. F. to 30.degree. F.; for when the moisture content of the food is rich in dissolved salts, the freezing point may be well below 32.degree. F. It is vital that the refrigeration, while close to freezing, not fall below the freezing point; for the formation of destructive ice crystals in the food must be avoided. It is also important to seal the trays to avoid the loss of moisture and volatile constituents.
If, therefore, the cartridges containing the trays have just been removed from the refrigerator before being placed in the hot-air oven, the oven must be capable of raising the food from, say 30.degree. F. to 150.degree. F. within a relatively short period so that the pre-cooked meals in all of the trays are then ready to be served. For this purpose, it is essential that the heating process be carried out in a manner whereby all trays are simultaneously raised in temperature at substantially the same rate, for otherwise the food in some trays may become overheated and others will be at a temperature below their proper service temperature.